About 15% of harbour porpoises found dead on beaches in the Netherlands has ingested plastic in the stomach. This is shown in a recent publication by Wageningen Marine Research and the Faculty of Veterinary Medicine (Utrecht University).
Dietstudy and plastic
Wageningen Marine Research has a long track record in study of the diet of beached harbour porpoises. Non-food items in the stomachs were recorded, but not following a strict method suitable dedicated to plastic monitoring. Following this early approach, about 7% of the animals were noted to have plastic in the stomach
In more recently analysed samples of stomachs the diet analyses were supplemented with the standard method used in the EU for monitoring plastic abundance in the stomachs of northern fulmars and marine turtles. This addition implies that all stomach contents are filtered over a 1mm sieve and studied under the microscope. Using this standard approach, plastics were recorded in 15% of the animals.
Studies from other countries bordering the North Sea report far less plastics, at most 1 to 2%. But usually those studies only visually inspected stomachs during autopsies. In order to obtain a proper view of regional differences or trends over time, the standard method with the 1mm sieve will be necessary.
The findings suggest that harbour porpoises mainly accidentally ingest plastics when foraging on fish close to the bottom. In many cases, harbour porpoises that contained plastics, had also ingested other natural bottom debris, such as shell fragments and bog-wood (semifossil wood derived from old surfaced peat layers in the bottom of the North Sea). Stomach contents of northern fulmars mainly reflect plastics pollution near the water surface, but harbour porpoises, like seals could thus act as an relative indicator for plastic abundance near the bottom of the sea.
Citation and downloads
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